1. Field of the Invention
The present invention relates to a scribing method for forming a groove and a cut-off line on a workpiece and a blasting machine used for the scribing. More specifically, the present invention relates to a scribing method by blasting that ejects an abrasive together with compressed gas and a blasting machine used for the method.
2. Description of the Related Art
A scribing, which forms a groove and a cut-off line on a workpiece, is used to form a groove serving as a break starting point when a hard brittle material such as a glass is cut. The scribing is also used to cut and divide a conductive film and a semiconductor film formed on a substrate into a predetermined pattern during fabrication of a semiconductor device or similar case.
The following describes an exemplary solar cell as one example of the semiconductor device. A solar cell panel includes a conducting layer, a photoelectric conversion layer, a buffer layer, and a transparent electrode layer. The conducting layer is disposed on a glass substrate and serves as a rear surface electrode. The photoelectric conversion layer is formed on the conducting layer. The buffer layer and the transparent electrode layer are formed on the photoelectric conversion layer. Each time the conducting layer, the photoelectric conversion layer, the buffer layer, and the transparent electrode layer are formed on the glass substrate, each of the layers are scribed at a predetermined pattern to cut and divide them. This forms a plurality of solar cells serially coupled on the glass substrate and also includes an integrated structure.
As a method for the scribing, conventionally, a laser scribing, a mechanical scribing, and a scribing by sand-blasting method are available.
Among them, the laser scribing adjusts the focal point of the laser to a surface of a workpiece and slides the workpiece placed on a processing table or a laser oscillator according to a preliminarily programmed process pattern precisely to form a cut-off line in the predetermined pattern. A processing apparatus used for the laser scribing is complicated and expensive apparatus, thus requiring a considerable initial investment.
Moreover, since the laser scribing is a process using heat, the laser scribing may deform the workpiece or change the workpiece in quality, therefore, there is a restriction to applicable material or the like.
There is a difficulty in a process of a transparent material where adjustment of the focal point of the laser is difficult. Also, this may cause a dross (a weld deposit of a melted material) to malfunction of the product or similar failure.
Among the above-described scribing methods, the mechanical scribing, for example, forms a groove by contacting the surface of the workpiece while rotating a grinding wheel formed by a diamond grindstone or the like at high speed and cutting off the surface of the workpiece in a predetermined pattern. As the work proceeds, a tool such as expensive grinding wheel wears out, and process accuracy changes even the wear of the tool is slight, therefore, the tools are required to be exchanged frequently. This requires a considerable running cost and stop of work during exchanging the tool, reducing productivity.
Accordingly, there is a demand for scribing by a blasting machine. The blasting machine has a comparatively simple apparatus configuration and therefore can be introduced at low-price compared with a process apparatus using laser. Moreover, the handling is easy, and only replenishing or exchanging the abrasive is required. Accordingly, the blasting machine allows continuous scribing without suspending work and without changing the process accuracy.
In response to the demand, scribing the conductive film, the photoelectric conversion layer, the transparent electrode, or the like, which are performed during the manufacturing process of the solar cell by blasting is proposed (Japanese LOPI Nos. H09-260704 (JP1997-260704A) and JP2000-124490A).
Although not specialized in scribing, the applicant of the application has already proposed a disc-type apparatus for supplying a constant quantity of abrasives as an apparatus for supplying a constant quantity of abrasive 10. The apparatus for supplying a constant quantity of abrasive 10 aims to improve processing accuracy or the like by stably supplying a constant quantity of abrasive to an ejection nozzle in blasting. Then, the abrasives precisely measured by a measuring hole 13a disposed at a disc 13 which rotates in an abrasive tank, are supplied to an ejection nozzle 20 together with compressed gas (see FIG. 1 below, related art: JP5183089B2 for detail).
The groove portions formed in the conducting layer, the photoelectric conversion layer, and the transparent electrode layer by scribing in the above-described manufacturing process of solar cell are required to be formed thin as much as possible. This improves power generation efficiency because the groove part does not contribute to electric generation when formed to be a solar cell.
In response to the request, in both inventions described in the above-motioned '704 and '490, masking is performed to cover the surface of the workpiece other than a part forming a groove with a protective texture before scribing by blasting. This allows the grooves in the predetermined pattern to be formed on the surface of the workpiece.
Accordingly, in the above-described manufacturing example of solar cell, every time the conducting layer, the photoelectric conversion layer, the buffer layer, and the transparent electrode layer are formed, masking is required by a method such as printing of the protective texture in the predetermined pattern at high accuracy. Also, after scribing by blasting, removing the protective texture mounted during masking is required by washing or another method. If the grooves or the like can be formed at high accuracy by ejecting the abrasive directly on the surface of the workpiece by blasting without masking, some manufacturing processes can be omitted and the volume of the materials to be used can be reduced. Accordingly, scribing by blasting can be performed at further low cost, and drastic reduction in time taken for the work is achieved.
On the other hand, in the case where a groove is formed by blasting in the known method without performing the above-described masking and using the known blasting machine, a groove with a width equal to or less than 1 mm cannot be formed. There is no existing blasting method that allows forming a fine groove, which is required in the above-described manufacture of solar cell or the like, without masking.
The scribing performed in the manufacturing process of solar cell is described above. However, an advantage in cost by achieving scribing by blasting without masking and necessity of fine process accompanied by downsizing and weight saving of various products are also similarly demanded in a field other than manufacture of solar cell.
The present invention is made to solve the drawbacks in the above-described related art, and an object of the present invention is to provide a scribing method by blasting that allows forming a groove and a cut-off line on a workpiece at high accuracy without masking and a blasting machine used for the method.